Outdoor data underrate pollutant exposure.

A new study suggests that most people inhale substantially more organic contaminants, including cancer-causing benzene, than is indicated by standard environmental risk assessments based on outdoor measurements.

"Ambient measurements at central sites aren't good predictors of [personal] exposure," says John Adgate of the University of Minnesota in Minneapolis. "Actual exposures are higher."

To monitor urban air quality, environmental agencies typically measure pollutant concentrations in samples collected at centralized outdoor locations and extrapolate individuals' average exposures from those measurements. That's a reasonable approach for studying ozone and other pollutants that form out-of-doors or that come almost exclusively from identifiable industrial sources.

But for volatile organic compounds (VOCs), which arise from sources such as air fresheners, cleaning agents, and cigarette smoke, assessments of outdoor air quality misrepresent what's under people's noses, researchers now report. That's because many daily activities--including driving to work, visiting dry-cleaning shops, and sitting in smoky restaurants--put people in envelopes of air that are disproportionately laden with chemicals.

Adgate and his colleagues outfitted 71 nonsmoking volunteers in Minneapolis and neighboring St. Paul with lapel-mounted air filters that sopped up VOCs for 2 days. In the lab, the team then used gas chromatography to measure 15 specific VOCs. The researchers simultaneously sampled VOCs from a central location inside each volunteer's home and from a nearby exterior location.

For 14 of the VOCs, all of which are designated as hazardous by the Clean Air Act, the lapel sensors contained much higher concentrations than outdoor samples did. Indoor measurements tended to be intermediate. According to the lapel sensors, the median personal exposure to benzene was 3.2 micrograms per cubic meter, whereas outdoor and indoor concentrations were 1.3 [micro]g/[m.sup.3] and 1.9 [micro]g/[m.sup.3] respectively. Life-long exposure to 1.3 [micro]g/[m.sup.3] of benzene in air is considered enough to cause 10 cancers in a million people, whereas 3.2 [micro]g/[m.sup.3] would correspond to 25 cancers.

Outdoor and indoor benzene concentrations have fallen in recent years, a result of declines in cigarette smoking and of regulations that permit less benzene in gasoline and consumer products, says Lance Wallace of the Environmental Protection Agency in Reston, Va. Nevertheless, he adds, the new study suggests that nonsmokers' personal exposures are surprisingly high.

Among the VOCs that Adgate and his team studied were chloroform, a by-product of chlorination that's released from household water; d-limonene and a- and b-pinene, common deodorizing chemicals that produce scents of lemon and pine; para-dichlorobenzene, an air freshener and pesticide; and tetrachloroethylene, which emanates from dry-cleaned clothing. Median concentrations of these compounds in personal air ranged from about 3 times to nearly 60 times those found in outdoor air, the researchers report in an upcoming Environmental Science and Technology.

Fortunately, says Wallace, "it's easy ... to do something about it." Excess personal exposure can be minimized by avoiding cigarette smoke, air fresheners, and long automobile commutes and by using cleaning agents and other chemicals only in well-ventilated areas.